Arctic Mixotrophic Protists

The ecological impact of mixotrophic algae in a changing Arctic marine climate

While diatoms are the dominant primary producers in many Arctic marine environments, it is the ability of the mixotrophic pico- and nanophytoplankton to both photosynthesize and consume a significant proportion of the bacterial biomass that draws our attention. This aspect of the microbial community tends to be poorly understood both qualitatively and quantitatively, largely due to difficulties of in situ identification of the diverse taxa that are mixotrophic algae.

The goals of this project are to: 1) examine the physiology of strains of different algal groups – chlorophytes (Micromonas, Pyramimonas), stramenopiles (Dinobryon, Pedinella, Helicopedinella), haptophytes (Prymnesium, Pavlova) and a cryptophyte (Geminigera) that have been identified as mixotrophic and occur in the Arctic – including an examination of how changes in temperature and dissolved nutrients affect photosynthesis versus irradiance and bacterivory; 2) relate grazing rates to the abundance of the Arctic species determined using qPCR and environmental DNA samples previously collected throughout the Arctic to estimate grazing impact; and 3) evaluate differential gene expression in cultures where grazing is high versus low for a subset of species from each of the major groups. Size structure plays a major role in determining carbon flux in planktonic ecosystems. Consequently, if Arctic warming does increase dominance of smaller phytoplankton as some researchers have proposed, the previously unsuspected importance of these organisms as predators of bacteria will contribute to altering the Arctic food web.